This invention relates to a method and an apparatus for visualizing elastic waves which propagate in a solid substance. Here, a solid substance means an elastic body (for example, metal, concrete, synthetic resin, glass, or the like). An elastic wave means a wave of elastic oscillation which propagates in the elastic body.
Heretofore, a typical method for visualizing elastic waves in the solid substance included a visualization method for the elastic waves which utilizes a principle of photo-elasticity and a visualization method which measures a displacement of an exterior of the solid substance by utilizing a laser displacement meter.
First of all, the visualization method for the elastic waves which utilizes the principle of photo-elasticity is a method which measures a stress generated in the solid substance upon elastic wave propagation therein in accordance with the principle of photo-elasticity. The first method can visualize a behavior of a wave front of an instantaneous elastic wave by synchronizing a timing of elastic wave radiation with a timing of flashing a stroboscopic lamp. It is also possible to visualize a behavior of elastic wave propagation by varying the timings.
The second visualization method which measures a displacement of an exterior of the solid substance by utilizing a laser displacement meter is a method which measures a displacement of the solid substance upon elastic wave propagation on a surface or an interior of the solid substance from the outside by means of the laser displacement meter. The second method can visualize a behavior of a wave front of an elastic wave by synchronizing a timing of elastic wave radiation with a timing of measuring the displacement and by measuring a displacement distribution while scanning a sensor.
The first photo-elasticity method is limited to a subject substance which is a transparent body having a photo-elasticity effect (for example, glass, synthetic resin, or the like) and cannot measure a transverse wave (SH wave). The second laser method is limited to a substance which is an opaque body since a laser must be reflected and cannot detect transverse waves (SV waves) and surface waves.
Accordingly, an object of the present invention is to provide a method and an apparatus for visualizing an elastic wave propagation in a solid substance, that can be applied to a subject substance which is any one of a transparent body and an opaque body and that can detect SV waves (transverse waves) and SH waves (transverse waves) in elastic wave motion modes, and longitudinal waves, surface waves, and creeping waves.
Here, a longitudinal wave means a progressive wave in which an oscillating direction of a medium particle coincides with an oscillating direction of propagation. A transverse wave means a progressive wave in which an oscillating direction of a medium particle is perpendicular to an oscillating direction of propagation. An SV wave means a wave (a kind of transverse wave) generated by bringing a longitudinal wave into incidence into a specimen. An SH wave means a wave (a kind of transverse wave) generated by applying to a specimen an external force which horizontally rubs a surface of the specimen. A creeping wave is generated by bringing a longitudinal wave into incidence into a specimen at a critical angle of a longitudinal wave (a first critical angle) and is a longitudinal wave which progresses straightly along a surface of a specimen.
In order to achieve the above object, a method for visualizing elastic wave propagation in a solid substance in accordance with the present invention comprises the following steps of:
(1) generating elastic waves in a solid substance in response to electric signals;
(2) measuring a quantity of stress change in the solid substance in connection with elastic wave propagation in the solid substance;
(3) synchronizing a transmission timing of the electric signals with a measurement timing of the stress change;
(4) carrying out measurement while scanning a sensor; and
(5) imaging wave fronts of the elastic waves propagated in the solid substance by synchronously indicating the stress change as a function of time.
The visualization method of the present invention may further comprises the steps of (6) delaying the imaging step; and (7) imaging a propagating condition in the elastic waves propagated in the solid substance by changing a delay time.
The quantity of stress change can be detected as a voltage change by a voltage sensor. Also, the stress change can be detected as a displacement in the solid substance by an electromagnetic sensor.
The visualization method can be applied to a ultrasonic flaw detecting method for detecting a flaw in a metal material by transmitting ultrasonic waves into a welded portion of austenitic steel (for example, an austenitic stainless steel, a nickel base high alloy, or the like). Also, a condition of elastic wave propagation in a metal material can be simulated by applying the visualization method to a transparent elastic body.
An apparatus for carrying out the method for visualizing elastic wave propagation in a solid substance comprises: an elastic wave generator for generating elastic waves in a solid substance in response to electric signals; an electric signal transmitter for transmitting electric signals to the elastic wave generator; a sensor for measuring elastic waves propagated in the solid substance; a sensor scanner for controlling a scanning position of the sensor; a detected-signal recorder for receiving and recording detected-signals from the sensor; a synchronizing circuit for sending the detected-signals from the sensor to said recorder in synchronization with timing signals from the sensor scanner and electric signal transmitter; and an elastic wave stress distribution display for imaging stress distribution signals of the detected-signals from the detected-signal recorder.
The visualization apparatus may further comprise a delay circuit for sending delay time signals to the elastic wave stress distribution display. In the visualization apparatus, a wedge member may be attached to a distal end of the sensor in order to measure a small region of area.
The visualization apparatus can be applied to an ultrasonic flaw detecting method for detecting a flaw in a metal material by transmitting an ultrasonic wave into a welded portion of an austenitic steel (for example, an austenitic stainless steel, a nickel base high alloy, or the like). Also, a condition of elastic wave propagation in a metal material can be simulated by applying the visualization method to a transparent elastic body.